It is known in the art that the weight of an aircraft on the ground can be measured by various means. For example, the weight of a fixed wing aircraft is typically measured on the ground by weight scales or by a weight on wheels (WOW) device, or in the case of a helicopter, weight is typically determined by manually tracking fuel, cargo, and passenger weight.
For fixed wing aircraft, a change in weight after takeoff is primarily due to fuel consumption, therefore, automatic weight tracking can be easily performed by known means. However, a helicopter can have significant weight changes imposed on the vehicle once in flight, and without landing again, by on-loading and off-loading passengers, e.g., ground troops, by lifting external loads, e.g., land vehicles, or by in-flight refueling or fuel dumping. These unique requirements render conventional techniques of weight sensing inadequate and necessitate a method for accurately determining the weight of the helicopter while in flight.
In a helicopter, there are certain components, e.g., rotor shaft, pitch control horn, and rotor head spindle, that experience stress which varies due to aircraft weight and other factors. Tracking these stresses over time aids in determining the useful life of these components. Direct monitoring of such components by strain gages or similar devices is impractical because of the need for slip ring apparatus which is inherently complex and prone to failure. However, accurately knowing the gross weight of the vehicle along with other flight parameters allows the calculation of stress, and thus the calculation of useful (or safe) life of the aforementioned components. Knowing the safe life of these components helps avoid the cost of premature maintenance and the hazards of breakdown during operation.
Additionally, the ability to sustain a hover (i.e. maintaining steady level flight with no vertical or horizontal motion) varies as a function of flight parameters such as air density, temperature, and vehicle weight. For example, at a given altitude, temperature, and gross weight, the helicopter may have no difficulty sustaining a hover. However, if the altitude or temperature increases, the air density will decrease and a hover may not be sustainable at the new condition. Therefore, accurate weight measurement during flight also allows a wider range of mission profiles, passenger or equipment deployment, and hover maneuvers within the permissible flight envelope.